In U.S. Pat. Nos. 4,608,040, 4,776,833, 5,222,933, 5,421,806, 5,230,797 and 5,338,284 of Benjamin Knelson and now assigned to the present Assignee is disclosed a centrifugal separator of the type including a rotatable bowl having a peripheral wall of generally frusto-conical shape on which is provided a plurality of axially spaced, annular recesses. The particulate material containing fractions of different specific gravity to be separated is fed in slurry form through a feed duct to a position at or adjacent a base of the bowl so that the feed materials flow outwardly onto and pass over the peripheral wall with heavier particulate materials collecting in the annular recesses while lighter particulate materials escape from the bowl through the open mouth. In the above patents, all of the annular recesses are fluidized by the injection of fluidizing water through holes in the peripheral wall at the respective recesses thus acting to fluidize the collecting material within the recesses.
A further arrangement is disclosed in U.S. Pat. No. 5,586,965, issued Dec. 24, 1996 of the above inventor in which the number of recesses is reduced and a frusto-conical lead-in section of the bowl is provided which is free from fluidized recesses so that the feed material is deposited onto the lead-in section and flows over that lead-in section prior to reaching the first annular recess. In this arrangement there are provided discharge ports at the base of the recess or recesses which are opened by valves periodically so that the concentrate is discharged from the recess on an effectively continuous basis as opposed to the batch collection basis of the above patents.
In U.S. Pat. No. 5,601,523 issued Feb. 11, 1997 of the above inventor there is disclosed a continuous machine of the above type where at each discharge port is provided a guide body which is generally a spherical ball located in the recess in front of the port. The balls are supported by a ring which extends around the recess at the mouth of the recess.
Further developments of this continuous machine are shown in U.S. Pat. No. 6,149,572 issued Nov. 21, 2000 where at each discharge port each spherical ball is located in the recess in front of the port by a support bar which extends across the recess.
It is also known, as shown in a brochure of a machine manufactured under the above patents to provide a diffuser ring which extends around the recess at the mouth leaving gaps between the top and bottom of the ring and the edge of the recess through which the heavier materials pass for collecting in the recess and for discharge through the ports as the valves are opened.
A further arrangement is disclosed in U.S. Pat. No. 5,895,345, issued Apr. 20, 1999 of the above inventor in which the amount of fluidizing water is reduced by supplying water only to some of the recesses of the bowl which are reduced in depth. This includes a lowermost section of the wall which has no fluidized recesses in a row of the shallower non-fluidized recesses.